1. Field of the Invention
The present invention relates to silos for storing granular material, such as bulk products or cereals, for example.
2. Description of the Prior Art
Silos have been proposed with a suspended head, which although rendering it possible to avoid the need for a mechanical means for complete emptying by gravity, has the disadvantage of a substantial less useful volume in view of the presence of the head. A diameter of ten meters is rarely exceeded with a suspended head for cylindrical silos, and of 4 to 5 meters for rectangular silos.
This is the reason why preference is given to a silo design having a flat base joined to a substantially vertical side surface. A design of this nature allows a considerable gain of useful storage space, but requires mechanical emptying means, which becomes of greater size the greater cross-section of the silo.
It has been proposed to suspend an endless screw of the single or double acting type, by means of a pulley block connected to the roof of the silo, whereby the screw can be lowered onto the flat base of the silo to convey the material towards the discharge openings: this is the so-called "through-scraper" system. A system of this kind is, however, bulky, requires modifications to the roof of the silo and renders it possible to cope with no more than one silo at a time.
A system for use with a group of silos has been proposed and which for each silo comprises a diametral or lateral tunnel joined at right angles and at either side by ventilation ducts comprising "flaps" for guiding air flows. The granular material is thus fluidized close to the base and channelled between two adjacent ducts and against the walls of the ducts towards the tunnel until it is discharged below the tunnel by means of a mechanical conveyor. This system is, however, also bulky. In the case of cylindrical silos having diameters of ten meters, provision must be made to install on the base a very sizable tunnel joined at either side of the said tunnel by 9 ducts which requires approximately 72 meters of ducting and 36 ports leading to a central conveyor. Consequently, if a greater silo cross-section is contemplated, the ventilation equipment reaches a prohibitive cost because the pressure losses become substantial.
Each of these systems has the substantial disadvantage of leaving residual material behind in the silo which requires cleaning and sweeping out when different materials are to be subsequently stored in the silo.